The present invention relates to a system for driving a liquid crystal matrix display panel, and more particularly to a system for driving the display panel so as to reproduce an image with a gray scale.
In a television with a passive matrix liquid crystal display panel each pixel of which does not contain an active element, the display panel is driven to produce pictures with a gray scale using an amplitude selection method.
Explaining a conventional driving system with reference to FIG. 2 showing a driving voltage waveform applied to a pixel at the intersection of a data electrode and one of the scanning electrodes of a display panel , a reference Tw shows a select period for selection of a pixel and Ts is a non-select period. In the non-select period Ts, a bias voltage is applied to the pixel in a waveform having an amplitude of .+-.V1. In the select period, opposite driving pulses D are applied to the pixel. The driving pulse D comprises a lower driving voltage of .+-.V2 and higher driving voltage of .+-.V3. The half tone of the picture is decided by the ratio of the period of time for the higher voltage .+-.V3 to the period of time for the lower voltage .+-.V2. However, in such a driving system, crosstalk occurs in the picture on the display panel, as described hereinafter in detail.
FIG. 3 shows a matrix arrangement of data electrodes S1 to Sn and scanning electrodes T1 to Tm for a liquid crystal display panel. FIG. 4a shows a driving voltage waveform applied to a scanning electrode T2, for driving pixels 100 and 102 of FIG. 3. FIGS. 4b and 4c show driving voltage waveforms applied to data electrodes S2 and S3. Capacitance connections between the scanning electrode T2 and data electrodes S2 and S3 noise which produce spike-shaped noise components 1 to 18 in the waveforms as shown in FIGS. 4a to 4c.
Noise components 1, 3, 5, 7, 9, and 11 are formed due to noise induced in the scanning electrode T2 by voltage variations of the waveform for the data electrode S2 shown in FIG. 4b. Noise components 2, 4, 6, 8, 10, and 12 are formed by voltage variations of the waveform of FIG. 4c for the data electrode S3. On the other hand, components 13 to 18 are formed in the waveforms for the data electrodes S2 and S3 by voltage variations in the waveform for the scanning electrode T2.
FIG. 4d shows a waveform for driving the pixel 100, which is the difference between the voltage waveforms of FIGS. 4a and 4b. FIG. 4e shows a driving vaveform for the pixel 102, which is formed by the difference between voltage waveforms of FIGS. 4a and 4c. It will be seen that the pulse of the higher voltage .+-.V3 for determining the tone is formed by the leading edge of the selection pulse S in the waveform for the scanning electrode and the leading edge of the pulse P of the waveform for the data electrode shown in FIG. 4b (4c). In the waveform of FIG. 4d, the effective value of the pulse of the higher voltage .+-.V3 is reduced to a smaller than optimum effective value shown by a dotted line. To the contrary, the effective value of the pulse of the higher voltage in the waveform of FIG. 4e becomes larger than an optimum effective value shown by a dotted line. The deviation of the effective value from the optimum effective value is integrated, which causes large crosstalk.